- Tandem Acid/Pd-Catalyzed Reductive Rearrangement of Glycol Derivatives
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Herein, we describe the acid/Pd-tandem-catalyzed transformation of glycol derivatives into terminal formic esters. Mechanistic investigations show that the substrate undergoes rearrangement to an aldehyde under [1,2] hydrogen migration and cleavage of an oxygen-based leaving group. The leaving group is trapped as its formic ester, and the aldehyde is reduced and subsequently esterified to a formate. Whereas the rearrangement to the aldehyde is catalyzed by sulfonic acids, the reduction step requires a unique catalyst system comprising a PdII or Pd0 precursor in loadings as low as 0.75 mol % and α,α′-bis(di-tert-butylphosphino)-o-xylene as ligand. The reduction step makes use of formic acid as an easy-to-handle transfer reductant. The substrate scope of the transformation encompasses both aromatic and aliphatic substrates and a variety of leaving groups.
- Ciszek, Benjamin,Fleischer, Ivana,Kathe, Prasad,Schmidt, Tanno A.
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supporting information
p. 3641 - 3646
(2020/03/25)
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- Asymmetric Transfer Hydrogenation of 1,3-Alkoxy/Aryloxy Propanones Using Tethered Arene/Ru(II)/TsDPEN Complexes
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A series of propanones containing combinations of aryloxy and alkoxy substituents at the 1- and 3-positions were reduced to the alcohols via asymmetric transfer hydrogenation using a tethered Ru(II)/TsDPEN catalyst. The enantioselectivities of the reductions reveal a complex pattern of electronic and steric effects which, when used in a matched combination, can lead to the formation of products of up to 68% ee (84:16 er) from this highly challenging class of substrate.
- Forshaw, Sam,Matthews, Alexander J.,Brown, Thomas J.,Diorazio, Louis J.,Williams, Luke,Wills, Martin
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supporting information
p. 2789 - 2792
(2017/06/07)
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- Highly efficient synthesis of functionalized α-oxyketones: Via Weinreb amides homologation with α-oxygenated organolithiums
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An efficient, chemoselective homologation of Weinreb amides to the corresponding variously substituted α-oxyketones has been developed via the addition of lithiated α-oxygenated species. This one-step, experimentally easy, high yielding protocol is amenable not only for accessing simple α-oxyketones but also for more complex substituted ones ranging from primary and secondary alkyl-type to aromatic ones. Full delivery of the stereochemical information contained in the starting materials is observed through both the employment of enantioenriched Weinreb amides and optically active organolithium species.
- Pace, Vittorio,Murgia, Irene,Westermayer, Sophie,Langer, Thierry,Holzer, Wolfgang
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supporting information
p. 7584 - 7587
(2016/07/06)
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- Ring-opening reactions of epoxides catalyzed by molybdenum(VI) dichloride dioxide
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Transformation of epoxides to β-alkoxy alcohols, acetonides, and α-alkoxy ketones is achieved by using molybdenum(VI) dichloride dioxide (MoO2Cl2) as a catalyst. Alcohol, aldehyde, oxime, tosyl, and tert-butyldimethylsilyl functional groups are tolerated during the methanolysis and acetonidation of the functionalized epoxides. No polymerization product is observed with any of the epoxides. Direct conversion of epoxides devoid of sensitive functional groups into the corresponding α-methoxy ketone is achieved in a single step by using the MoO2Cl 2/Oxone system. Georg Thieme Verlag Stuttgart.
- Jeyakumar, Kandasamy,Chand, Dillip Kumar
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p. 807 - 819
(2008/09/21)
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- Stereoselectivity of Baker's yeast reduction of 2-propanones: influence of substituents.
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The stereoselectivity of Baker's yeast reduction of prochiral alpha-oxygenated 2-propanones has been studied by varying the substrate structure. The 1-hydroxy-3-methoxy-3-propanone 1a was reduced to the corresponding alcohol (R)-2a with 88% enantiomeric excess. Replacing the hydroxy group in 1a with phenoxy or benzyloxy (1b and 1c) gave the alcohols (S)-2b and (S)-2c with 53 and 32% ee, respectively. Reduction of the methyl ketone 1d gave the alcohol (S)-2d with 91% ee. Attempts to improve the enantioselectivity of the reduction of 1c by lowering the substrate concentration or addition of selective reductase inhibitors had only small effect on the enantioselectivity.
- Waagen,Partali,Hollingsaeter,Huang,Anthonsen
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p. 506 - 510
(2007/10/02)
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